Anybody who is in the healing profession now agrees that there is direct connection between our emotional health and our physical health. It has been established for a long time that our body affects our emotions (if you have cancer, there is a big chance that you get depressed); but it was only fairly recently when it was accepted that our emotions will cause some physical illnesses.
A field called psychosomatic medicine is engaged in studying the relationships of social, psychological, and behavioral factors on bodily processes and health. Our minds have influence over physical processes that it can cause some body systems to bog down. Conversely, it can also improve our health in a process called autosuggestion or positive thinking. This study combines psychiatry, psychology, neurology, surgery, allergy, dermatology and psychoneuroimmunology.
But, fact is, this system has been practiced in some cultures for ages. The Chinese has known these psycho-physical connections for centuries now, for example. But in the western world, we owe this discovery to the pioneering works of scientists like Franz Alexander, Sigmund Freud, and Thure von Uexküll and his colleagues who developed the biosemiotic theory which is the main theoretical basis for psychosomatic medicine.
These works three ways:
a. Some physical diseases are known to have mental components from the stresses of everyday living, such as lower back pain and high blood pressure.
b. Some physical diseases are directly caused by stress such as Irritable Bowel Syndrome, peptic ulcers, etc.
c. And there are illnesses called somatoform disorders which the World Health Organization defines din the International Statistical Classification of Diseases and Related Health Problems. There are people with mental disorders who imagine that they have physical illnesses even if none exists.